This reminds me of the old joke....
Guy says to a girl: "Would you fuck me for a million bucks?"
Girl: "A million bucks? Really?"
Guy: "Yup, a million bucks!"
Girl: "Well, for a million bucks, yeah."
Guy: "How about fifty bucks?"
Girl: "Fifty bucks! What do you think I am, a prostitute!!???!!"
Guy: "We already established what you are, now, we're just talking price."
If you are fucking for money, then you're a pro. Do it if it feels right to you, if not, don't.